1. Field of the Invention
This invention relates in general to an apparatus for extracting light transversely from a light guiding system, and more particularly, to a front light extraction tape applicable to surfaces of waveguides for extracting light therefrom.
2. Description of Related Art
There has been an extensive effort to develop methods of extracting light transversely from optical waveguides, such as large core plastic optical fibers and slab waveguides. Optical waveguides having transverse light outputs may be used as extended light sources, such as may be used for backlighting an active liquid crystal display panel. The flexibility afforded by large core plastic fiber further permits the production of extended light sources having arbitrary shape.
There have been several attempts at coupling light out of the side of an optical waveguide. One method of coupling light transversely from a waveguide employs a number of prisms attached to the waveguide. The prisms have a refractive index the same as or higher than the refractive index of the waveguide. Thus, light which would normally be totally internally reflected by the waveguide is transmitted through the interface between the waveguide and the prisms, and directed away from the waveguide in essentially a transverse direction.
Several approaches have been followed in fabricating a transverse light extractor of this type. One known approach, disclosed in U.S. Pat. No. 5,396,350, includes securing prisms to a waveguide surface using an adhesive layer, and further securing the output surfaces of the prisms to a backing layer by a second layer of adhesive. Such a light extractor has a complex structure, having many layers and resulting in high reflective losses. The transverse light extractor is fabricated using photolithographic techniques, which are not well suited to fabricating nonplanar devices. This limits the shape of the light extractor, and restricts the applications where it can be used.
Another light extractor, disclosed in U.S. Pat. No. 5,521,725, comprises a spacer with prisms molded on a lower surface of the spacer and with lenses molded on an upper surface of the spacer. The light extractor uses a layer between the prisms and the waveguide to which it is attached for extracting light from the waveguide. Additionally, the prisms, spacer, and lenses are formed from the same material since the extractor is molded.
There is, therefore, a need for a transverse light extractor having a simpler structure than that of currently available transverse light extractors, in which there are fewer layers and the reflective losses are reduced. There is also a need for a transverse light extractor which is not limited to planar geometries, but which can be adapted to nonplanar geometries.
Additionally, there is a need for a light extractor which may be used without an extra layer between the extractor and the waveguide. Furthermore, there is a need for a light extractor which is simple in structure and which permits the prisms and the spacer to be formed form different materials.